The invention relates to the field of treatment and care of laundry items, where in particular for drying purposes the laundry items are impinged upon by air-conveyed heat. It relates to an exhaust air dryer with a process airflow entering from outside as supply air, which removes moisture from laundry introduced into a treatment compartment, and which exits to the outside through an air outlet as exhaust air, with at least one heat exchanger arranged between the treatment compartment and the air outlet, seen in the airflow direction, which removes heat from the process airflow while forming condensate.
Such an exhaust air dryer is known from DE 30 00 865 A1. This exhaust air dryer enables at least partial recovery of heat from the exhaust air flowing from the laundry to be dried. This property of the exhaust air dryer, which is per se advantageous, is however achieved at the cost of the precipitation of condensate from the exhaust air in the heat exchanger, at which a transfer of heat from the exhaust air to the supply air takes place, said precipitation having to be collected and disposed of. Although it is true that this is also customary in the case of tumble dryers of other types, it means a noteworthy and under certain circumstances scarcely welcome complication of the operation of this exhaust air dryer.
Various tumble dryers for the drying of laundry have become known, which operate according to two methods differing in principle, namely according to the condensation procedure or the exhaust air procedure.
Condensation tumble dryers are in widespread use, and are popular in terms of energy-related aspects. Here the laundry to be dried is introduced into the stream of heated process air. The laundry can here be located in a drum or also in a static drying compartment, as described, for example, in DE 198 33 775 A1. After flowing through the drying compartment, which is also known as a treatment compartment, the moisture-laden process air is then passed through a condensation device, in which the moisture driven out of the laundry is separated out of the process air by means of cooling of the process air. The process air is located in a closed air circuit, and is then heated once more and conveyed to the treatment compartment.
It is characteristic of an exhaust air dryer that the process air fed in from outside as supply air is directed into the treatment compartment after heating, and there comes into contact with the laundry to be dried. After leaving the treatment compartment, the exhaust air stream flows out through an air outlet, transporting the absorbed moisture with it. A particular development of the exhaust air dryer is described in the aforementioned DE 30 00 865 A1. DE 10 2006 003 817 A1 describes a dryer and a method for the treatment of laundry, where both a variant of a condensation tumble dryer and an exhaust air dryer are described.
Exhaust air dryers of such a type are basically characterized by a particularly simple construction, though from the energy consumption perspective they are not optimal. Against this background, DE 10 2006 003 817 A1 mentions the use of a heat pump circuit, but without providing further details in connection with the exhaust air dryer. DE 10 2006 003 817 A1 further describes a moisture dispenser arranged downstream of the treatment compartment seen in the airflow direction, which serves further to reduce the temperature of the exhaust air, in order to realize comparatively high laundry treatment temperatures, without these high temperatures damaging the components located downstream of the process air. In the case of the exhaust air dryer, the user must regularly replenish the moisture dispenser, because otherwise the drying program is automatically terminated.
DE 195 08 244 A1 describes a condensation tumble dryer, in which the condensed water drips into a drip tray and is pumped into a condensate collector receptacle. In order to avoid relatively demanding fill-level monitoring of the collector receptacle and interruption of the drying process should the collector receptacle overflow, DE 195 08 244 A1 proposes that in the event of a malfunction—that is to say in the case of the undesired overflow of condensate fluid from the collector receptacle—this condensate fluid be fed into the cooling air or into the process circuit of the condensation tumble dryer. However in order to permit operation of this type in the event of a malfunction, the cooling air guide must be embodied accordingly and be able to discharge the used cooling air to a location which is not sensitive to moisture.
Finally a tumble dryer is known from DE 103 02 864 A1 which can be switched between circulation mode operation (as a condensation tumble dryer) and exhaust air operation, depending on the laundry to be treated, where the exhaust air operation preferably serves to freshen up and air laundry. In order that in the circulation mode too, additives sprayed into the treatment compartment are activated, or water can be used as heated steam for the purposes of disinfection, then in the case of the known dryer operating as a condensation tumble dryer, the condensate can be fed to a spray device, which sprays this into the treatment compartment (laundry drum) as steam or mist. In exhaust air mode on the other hand, the exhaust air duct is closed in the direction of the heat exchanger, and the process air instead flows out of an opened exhaust air flap, so that the air flow does not circulate.